The production of nitrogen oxides (NOx) by internal combustion engines are undesirable and in many cases are controlled by regulations established by governmental entities. Furthermore, spark ignited engines exhibit abnormal combustion phenomena called “knock”, which occurs when combustion reactions in the unburned zone initiate rapid uncontrolled combustion prior to the arrival of the propagating flame front of a homogenous combustion process. Various methods have been employed in attempts to address knock, including lowering the end gas temperature such as by lowering the compression ratio, retarding the start of combustion, or providing evaporative cooling through direct injection. Another method involves modifying the octane rating of the fuel, such as by using a higher octane fuel. Yet another method for controlling knock includes increasing the flame propagation rate by, for example, improving the mixture homogeneity or by increasing the turbulence level induced by organized charge motion.
Another technique for knock suppression is exhaust gas recirculation. Such recirculation can occur from one or more exhaust gas recirculation (EGR) cylinders whose exhaust output is dedicated during at least part of the engine operation to continuously provide an EGR flow to the intake. Since the exhaust from such EGR cylinders does not escape the engine during EGR operation, alternate combustion processes in the EGR cylinders, such as a rich combustion operation, can be used to produce favorable species, such as hydrogen, in the exhaust output that is recirculated to the intake for all cylinders.
When the EGR cylinders operate to provide EGR flow and the remaining cylinders provide the exhaust output, the engine acts as a positive displacement pump to drive the EGR flow, reducing pumping losses in transporting exhaust to the intake system and allowing a wide range of engine out nitrous oxide emissions to be achieved. However, there is a pumping mean effective pressure (PMEP) penalty that results from obtaining a proper mix of EGR flow with fresh air flow in the intake in order to reduce cylinder-to-cylinder variation in the recirculated exhaust gas. Thus, problems remain in obtaining a proper mix of the EGR flow with the intake air flow over a wide range of engine operating conditions while achieving distribution of the EGR flow among the engine cylinders. Therefore, systems, methods and devices are needed to improve EGR flow in internal combustion engine systems.